Wireless communications systems are used in a variety of telecommunications systems, television, radio and other media systems, data communication networks, and other systems to convey information between remote points using wireless transmitters and wireless receivers. A transmitter is an electronic device which, usually with the aid of an antenna, propagates an electromagnetic signal such as radio, television, or other telecommunications. Transmitters often include signal amplifiers which receive a radio-frequency or other signal, amplify the signal by a predetermined gain, and communicate the amplified signal. On the other hand, a receiver is an electronic device which, also usually with the aid of an antenna, receives and processes a wireless electromagnetic signal. In certain instances, a transmitter and receiver may be combined into a single device called a transceiver.
Transmitters, receivers, and transceivers often include components known as oscillators. An oscillator may serve many functions in a transmitter, receiver, and/or transceiver, including generating local oscillator signal (usually in a radio-frequency range) for upconverting baseband signals onto a radio-frequency (RF) carrier and performing modulation for transmission of signals, and/or for downconverting RF signals to baseband signals and performing demodulation of received signals.
To achieve desired functionality, wireless communications elements must often have designs that produce precise operating characteristics. For example, it is often critical that oscillator circuits in wireless communication elements operate independently of the temperature of the oscillator circuit, to prevent variations in temperature from leading to undesired variations in the frequency of oscillation of an oscillator circuit. Accordingly, temperature compensated oscillator circuits have been employed to provide for temperature-independent operation. As another example, it is often critical that oscillator circuits avoid other effects, including integral nonlinearity (INL) occurring in digital-to-analog converters associated with an oscillator. In general, integral nonlinearity is a term describing the maximum deviation between the ideal output of a DAC and the actual output level (after offset and gain errors have been removed). The term is often used as an important specification for measuring error in a digital-to-analog converter.
In many wireless communication elements, the overall effective INL experienced by a DAC used in a frequency control circuit in a wireless communication elements is often dependent upon the composite of the voltage linearity of the DAC and the voltage to frequency linearity of an oscillator (e.g., a voltage controlled temperature compensated crystal oscillator) driven by the DAC. In many cases, designers of the DAC and other components of the wireless communication element may desire to reduce the overall effective INL, but may have no control over the voltage to frequency linearity of an associated oscillator (e.g., the oscillator may be manufactured or provided by a party other than the DAC designer).